review
The effects of outdoor air pollution on the respiratory health of Canadian children: A systematic review of epidemiological studies Laura A Rodriguez-Villamizar MD MSc1,2, Adam Magico BSc PhD3, Alvaro Osornio-Vargas MD PhD3, Brian H Rowe MD MSc1,4 LA Rodriguez-Villamizar, A Magico, A Osornio-Vargas, BH Rowe. The effects of outdoor air pollution on the respiratory health of Canadian children: A systematic review of epidemiological studies. Can Respir J 2015;22(5):282-292. Background: Outdoor air pollution is a global problem with serious effects on human health, and children are considered to be highly susceptible to the effects of air pollution. Objective: To conduct a comprehensive and updated systematic review of the literature reporting the effects of outdoor air pollution on the respiratory health of children in Canada. Methods: Searches of four electronic databases between January 2004 and November 2014 were conducted to identify epidemiological studies evaluating the effect of exposure to outdoor air pollutants on respiratory symptoms, lung function measurements and the use of health services due to respiratory conditions in Canadian children. The selection process and quality assessment, using the Newcastle-Ottawa Scale, were conducted independently by two reviewers. Results: Twenty-seven studies that were heterogeneous with regard to study design, population, respiratory outcome and air pollution exposure were identified. Overall, the included studies reported adverse effects of outdoor air pollution at concentrations that were below Canadian and United States standards. Heterogeneous effects of air pollutants were reported according to city, sex, socioeconomic status and seasonality. The present review also describes trends in research related to the effect of air pollution on Canadian children over the past 25 years. Conclusion: The present study reconfirms the adverse effects of outdoor air pollution on the respiratory health of children in Canada. It will help researchers, clinicians and environmental health authorities identify the available evidence of the adverse effect of outdoor air pollution, research gaps and the limitations for further research. Key Words: Air pollution; Asthma; Children; Health effects; Respiratory tract diseases
O
utdoor air pollution is a global problem with serious effects on human health (1). In fact, it has been estimated that in 2011, approximately 80% of the world’s population was exposed to air pollution levels that exceeded WHO guidelines (2,3). Air pollution is a complex mixture of compounds that vary greatly depending on the emission sources. Typically, the so-called criteria air pollutants (CAP, which include particulate matter [PM], ozone [O3], lead [Pb], carbon monoxide [CO], sulphur oxides [SOx] and nitrogen oxides [NOx]), are monitored in surveillance air-quality networks. Interestingly, PM itself represents a complex mixture of particles of various sizes and concentrations of soil, metals, organics, inorganics, elemental carbon, ions and endotoxins, among other contaminants (4). Recently, the PM2.5 (PM size ≤2.5 µm in aerodynamic diameter) has been the focus of most outdoor air pollution and health studies due to its ability to penetrate the lung tissue and induce local and systemic effects (4). Based on findings for lung and bladder cancer, the International Agency for Research on Cancer recently classified outdoor air pollution,
Les effets de la pollution de l’air atmosphérique sur la santé respiratoire des enfants canadiens : une analyse systématique d’études épidémiologiques HISTORIQUE : La pollution de l’air atmosphérique est un problème mondial qui a de graves effets sur la santé humaine. Les enfants sont considérés comme très vulnérables aux effets de ce type de pollution. OBJECTIF : Mener une analyse systématique complète et à jour des publications sur les effets de la pollution de l’air atmosphérique sur la santé respiratoire des enfants du Canada. MÉTHODOLOGIE : Les chercheurs ont effectué des recherches dans quatre bases de données électroniques entre janvier 2004 et novembre 2014 pour évaluer l’effet de l’exposition aux polluants atmosphériques sur les symptômes respiratoires, les mesures de la fonction pulmonaire et l’utilisation des services de santé en raison de maladies respiratoires chez les enfants canadiens. Deux analystes ont procédé à l’analyse indépendante du processus de sélection et de l’évaluation de la qualité, au moyen de l’échelle de Newcastle-Ottawa. RÉSULTATS : Les chercheurs ont colligé 27 études hétérogènes sur le plan de la méthodologie, de la population, des conséquences respiratoires et de l’exposition à la pollution atmosphérique. Dans l’ensemble, les études incluses portaient sur les effets indésirables de la pollution de l’air atmosphérique à des concentrations inférieures aux normes canadiennes et américaines. Les effets hétérogènes des polluants atmosphériques étaient déclarés selon la ville, le sexe, la situation socioéconomique et le caractère saisonnier du problème. La présente analyse décrit également les tendances de la recherche à l’égard de l’effet de la pollution atmosphérique sur les enfants canadiens depuis 25 ans. CONCLUSION : La présente étude confirme de nouveau les effets indésirables de la pollution de l’air atmosphérique sur la santé respiratoire des enfants canadiens. Elle aidera les chercheurs, les cliniciens et les autorités en santé environnementale à repérer les données probantes sur les effets négatifs de la pollution de l’air atmosphérique ainsi que les lacunes et les limites de la recherche, et ce, en prévision de prochaines recherches.
as a whole, as a group 1 carcinogen (5). In addition, well-documented associations exist between outdoor air pollution and other health conditions including asthma, cardiovascular diseases, respiratory infections, adverse birth outcomes and additional cancers, such as leukemia (1,6,7). Children are considered to be highly susceptible to the effects of air pollution due to the immaturity of their immune system, the potential for developmental disruption, greater amount of time spent outdoors and, therefore, higher exposure levels, and a relatively high volume of air exchange relative to body mass (8,9). In fact, outdoor air pollution consistently shows an adverse effect on childhood respiratory health, especially on asthma outcomes, with a total estimated health care cost (among 34 countries, including Canada) of approximately US$1.7 trillion in 2010 (10,11). Asthma is one of the top 10 causes of years lost due to disability in male children worldwide (12). The effects of outdoor air pollution on asthma and other respiratory conditions have been the subject of study involving many adult and children populations in Canada and
1School
of Public Health, University of Alberta, Edmonton, Alberta; 2Department of Public Health, School of Medicine, Universidad Industrial de Santander, Bucaramanga, Colombia; 3Department of Pediatrics; 4Department of Emergency Medicine, University of Alberta, Edmonton, Alberta Correspondence: Dr Laura A Rodriguez-Villamizar, Department of Emergency Medicine, University of Alberta, 7.40 University Terrace, 8440-112 Street Northwest, Edmonton, Alberta T6G 2T4. Telephone 780-492-5489, fax 780-407-3982, e-mail [email protected] 282
©2015 Pulsus Group Inc. All rights reserved
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Air pollution and children’s respiratory health
elsewhere. Air pollution levels in Canada are relatively low and most Canadian cities experience extreme low temperatures. Thus, Canadian studies offer a unique opportunity to examine the effects of more moderate doses of air pollution compared with those experienced in many other nations (13). In addition, Canada boasts one of the highest percentage of foreign-born citizens (14), being a society of mixed languages, cultures and genetic diversity. Recent findings suggest that the influence of genetic diversity on the population’s susceptibility to air pollution is an important factor that should be considered in this field (15). In 2007, a systematic review of air pollution and children’s health in Canada analyzed the results of epidemiological studies published between January 1989 and December 2004 (16). From 11 studies over a 15-year period, the review identified associations between respiratory health effects and at least some CAP measurements. These associations were, however, often weaker than those reported in studies conducted in other countries. This was believed to be due to the lower levels of air pollution in Canada, the lower number of hours spent outdoors during the colder Canadian winters, as well as reduced levels of outdoor air pollution infiltrating into homes, which could act to reduce personal exposure to outdoor air pollution. The objective of the present study was to conduct a comprehensive systematic review of the literature reporting the effects of outdoor air pollution on the respiratory health of children in Canada. We focused on the literature published during the past 10 years to update the previous review, identify new findings on types of associations between air pollutants and childhood respiratory health, and evaluate differences in those associations across Canadian cities.
METHODS
An a priori systematic literature review protocol was developed. The research question addressed in the present review was: what is the effect of outdoor air pollution exposure on respiratory conditions in Canadian children? Respiratory conditions included respiratory symptoms, lung function measurements and the use of health services due to respiratory disease. Search strategy To increase sensitivity, the search strategy used in the previous review (16) was modified. Specifically, four electronic bibliographic databases (MEDLINE, CINAHL, Scopus and CAB abstracts) were searched (Appendix 1). In general, databases were searched with a combination of terms and derived key words including variation to the following basic terms: “air pollution”, “outdoor air pollution”, “asthma”, “respiration disorders”, “respiratory health”, “respiratory symptoms”, “child”, “adolesc”, “youth” and “Canada”. In the MEDLINE search, the names of 16 specific Canadian cities were included to increase search sensitivity. The search strategy was not restricted by language or publication type. A Google Scholar web search was conducted and references of relevant studies were scanned and selected as a complementary search strategy. Study selection and data extraction The criteria for selecting studies included: any observational analytic design; publication date between January 1, 2004 and November 30, 2014; population included and reported data for children up to 18 years of age residing in Canada; exposure(s) included any nonbiological outdoor air pollutant whether measured directly or inferred (ie, by proximity to roadways), with special interest in the CAP (CO, NO2, SO2, O3, and PM10 and PM2.5); and outcomes included health services use (HSU), lung function measurement or self-reported respiratory symptoms. Studies that included a subset or cohort of Canadian children in which the data for the Canadians were not presented separately were excluded. Two reviewers (LR-V and AM) independently screened the identified articles’ titles and abstracts to select the articles for full review, and reviewed citations that were found to be potentially relevant for inclusion. A third reviewer (AO-V) resolved disagreement. Articles selected for full review were screened in a second round to confirm that the inclusion criteria were met. Agreement was measured using kappa (κ) statistics. Data extraction was performed by two reviewers (LR-V and AM) and summarized in standardized tables.
Can Respir J Vol 22 No 5 September/October 2015
Figure 1) PRISMA flow diagram for selection of studies Quality assessment Study quality was assessed using the Newcastle-Ottawa Scale (NOS), which uses an eight-item rating system to evaluate the method of selection of participants, the exposure/outcome assessment, and comparability among study groups (17). Comparability was evaluated by controlling for potential confounders in terms of study design and the type of health effects under evaluation. The Cochrane NonRandomized Studies Methods Working Group recommends the use of the NOS, although the study of its psychometric properties remains in progress (18). The NOS quality scores range from 0 to 9 (0 to 4 = poor quality; 5 to 7 = moderate quality; 8 to 9 = high quality). The NOS has specific formats for cohort and case-control studies only. The cohort study form was used to evaluate noncohort longitudinal studies and the case control form to evaluate case-crossover and cross-sectional studies. Two reviewers (LR-V and AM) independently performed the quality assessment of the included studies and disagreements were discussed and resolved by consensus. Data analysis Descriptive results of the included studies are provided. While quantitative analyses using pooled measures and random effect models were planned, they could not be conducted due to heterogeneity among study populations (children’s age), outcomes and study designs. Kappa statistics and 95% CIs were generated using Stata version 11.1 (StataCorp, USA).
RESULTS
Search results The present review follows the PRISMA recommendations (19). As indicated in Figure 1, the systematic search identified 162 studies. After removing duplicates, initial screening with inclusion/exclusion criteria and full-text review, 27 studies were included. Studies were excluded for a variety of reasons, primarily because they did not report results on Canadian children. Reviewer agreement was substantial for identifying potentially relevant studies (disagreement 22%; κ=0.73 [95% CI 0.70 to 0.75]) and excellent for identifying included/excluded studies in full-text review (κ=0.91 [95% CI 0.78 to 1.00]). Study characteristics The 27 studies that met the selection criteria varied in design, study location, number and type of air pollutants considered, age of children population and respiratory outcome. Tables 1 and 2 summarize the main characteristics and results of the individual studies grouped according to respiratory outcome examined (20-46). Fifteen of the 27 studies included data from Ontario (20,21,24,26,27,29,31,32,35-39,42,44), five used British Columbia (BC) data (22,23,30,34,46), four used Quebec data (28,33,40,41),
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Table 1 Characteristics and results of included studies with health services use outcomes Reference; study location; and study period Lin et al, 2004 (34); Vancouver area; 1987–1998
Study design; study population and size
Pollutants (mean or median levels*) and methods assessing exposure
Respiratory outcome
Hospitalizations Time series study; Mean CO (960), SO2 (4.77), NO2 (18.65), O3 for asthma hospitalizations of (28.02), PM10 (NS), PM2.5 6–12 year olds; from (NS) from 1995-1998; BC Linked Health from monitoring Dataset (n=3822) stations
Adjustment for confounding factors
Study findings
Sex, temperature, RR of asthma hospitalizations in low SES relative humidity, group associated with: NO2 (male, 1-day lag): 1.16 (95% CI 1.06–1.28), NO2 (male 4-day lag): SES, day of the 1.18 (95% CI 1.03–1.34), SO2 (female 4-day week lag): 1.17 (95% CI 1–1.37), and SO2 (female 6-day lag): 1.19 (95% CI 1–1.42)
Yang et al, Case-crossover, Mean CO (700), O3 (14.3), Hospitalizations OR of respiratory hospitalizations associated NO2 (16.8), SO2 (3.5), for respiratory 2004 (46); with 3-day lag mean and max PM10-2.5: case-control and disease (includ- 1.22 (95% CI 1.02–1.48) and 1.14 (95% CI Greater Vancouver; time-series analyses; PM10 (13.3) and PM2.5 (7.7); from local 0.99–1.32), respectively; time-series analysis ing asthma) 1995–1999 first hospital admisgave weaker associations sions of 0–3 year olds, monitors excluding birth-related admissions (n=1610)
Sex, SES, day of the week, season, study year, season and influenza hospitalizations
Sex, temperature, pollutant interactions and seasonality
Lin et al, 2005 (35); Toronto; 1998–2001
Case-crossover design; Mean PM10 (20.41), PM2.5 Hospitalization (9.59), for respiratory hospitalizations of PM10-2.5 (10.86), infections 0–14 year olds CO (1160), SO2 (4.73), (n=6782) NO2 (24.54), O3 (38.06); from monitoring stations
Luginaah et al, 2005 (37); Windsor; 1995–2000
Time series and casecrossover design; hospitalizations 0–14 year olds (n=1602)
Hospitalizations Mean NO2 (38.9), SO2 (27.5), CO (1300), for respiratory PM10 (50.6), TRS (8), and disease coefficient of haze (0.5); from monitoring stations
Time Series RR: NO2: female 2-day lag: 1.19 Temperature, sex, (95% CI 1.002–1.411); SO2: female Current-Day: humidity, baromet1.11 (95% CI 1.011–1.221); CO: female 2-day lag: ric pressure, 1.07 (95% CI 1.001–1.139); Cross-over design seasonality OR: CO: female current day, 2-day lag and 3-day lag: 1.15 (95% CI 1.006–1.307), 1.19 (95% CI 1.020–1.379) and 1.22 (95% CI 1.022–1.459)
Dales et al, 2006 (25); 11 of the largest Canadian cities; 1986–2000
Time series study; hospitalizations of 0–27 day olds (n=8586)
Hospitalizations Mean NO2 (21.8), SO2 (4.3), CO (1.0), O3 for respiratory (17.0), and PM10 (NS); disease from monitoring stations (population weighted average)
Long-term temporal The percentage of variation for IQR increase trends, day of for all gasses combined was 9.61% (95% CI 4.52–14.7); individually: O3: 2.67 (95% CI 0.98– week effects, 4.39); NO2 2.48 (95% CI 1.18–3.8); SO2: 1.41 weather (95% CI 0.35–2.47); CO: 1.3 (95% CI 0.13–2.49) variables, other gases and PM10
Villeneuve et al, 2007 (45); Edmonton; 1992–2002
Case-crossover design Summer/winter ED visits for (time stratified); ED median PM10 (22.0/19.0), asthma PM2.5 (7.0/7.3), CO visits of 2–14 year (600/900), SO2 (2.0/3.0), olds (n=20,392) NO2 (17.5/28.5), O3 (38.0/24.3); from monitoring stations
Temperature, Positive association were observed in warm relative humidity, season and higher in 2–4 years: OR 5-day season, average: NO2 1.50 (95% CI 1.31–1.71), CO 1.48 (95% CI 1.27–1.72), PM2.5: 1.16 (95% aeroallergens, and CI 1.04–1.28) and PM10: 1.16 (95% CI 1.05– ED visits for 1.28); For 5–14 years: OR 5-day average: NO2: influenza 1.13 (95% CI 1.02–1.24), O3: 1.14 (95% CI 1.05–1.24), PM2.5: 1.10 (95% CI 1.02–1.17), PM10: 1.14 (95% CI 1.06–1.22); many of the 1- and 3-day lags were also significant during the warm season for various pollutants
Szyszkowicz et al, 2008 (43); Edmonton; 1992–2002
ED visits for Longitudinal study; Mean/median CO asthma 0–10 years ED visits (700/600), NO2 (21.9/19.7), SO2 (2.6/2.2), (n=18,891) O3 (18.6/17.8), PM10 (22.6/19.4), PM2.5 (8.5/6.2); from monitoring stations
Sex, temperature, Many positive associations were observed in relative humidity, the warm season; the higher percentage increase for each pollutant was: CO (2-day lag) day of the week male: 17.7% (95% CI 10.2–25.6), NO2 (2-day lag) male: 19.2% (95% CI 11.4–27.6), O3 (same day) female: 17.8% (95% CI 7.1–29.5), PM10 (2-day lag) male: 7.4% (95% CI 3.1–11.9), PM2.5 (same-day) female: 7.7% (95% CI 5.2– 10.3), O3 (1-day lag), PM10 (same-day), and PM2.5 (2-day lag) showed positive variations for some age/sex/season combinations
Burra et al, 2009 (20); Toronto; 1992–2001
Longitudinal study; family physician and specialists service claim records for 1–17 year olds (n=1,146,215)
Mean SO2 (9.7), NO2 (39.2), O3 (33.3) and PM2.5 (17.9); from monitoring stations
OR of hospitalizations for 6-day average exposure to: PM10-2.5: boys 1.15 (95% CI 1.02–1.3), girls 1.18 (95% CI 1.01–1.36); PM10: boys 1.25 (95% CI 1.01–1.54); NO2: girls 1.31 (95% CI 1.05–1.63); PM2.5, O3 and SO2 showed no associations
SES, temperature, Asthma RR for pollutants by SES quintiles (Q1/Q5) physician visits were: SO2: 1.005 (95% CI 1.000–1.010), NO2: barometric pres1.002 (95% CI 0.995–1.008), and PM2.5: sure, 24 h mean 1.006 (95% CI 0.997–1.015); low SES groups relative humidity, had higher RR in SO2 and PM2.5 models day of the week
Continued on next page
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Air pollution and children’s respiratory health
Table 1 – CONTINUED Characteristics and results of included studies with health services use outcomes Reference; study location; and study period
Study design; study population and size
Smargiassi et al, Case-crossover 2009 (41); design (time Montreal (Quebec); stratified); 2–4 year 1996-2004 olds living near a refinery (n=1579)
Pollutants (mean or median levels*) and methods assessing exposure
Respiratory outcome
Asthma ED Daily peak mean SO2 (east/southwest of visits or refineries) using monitorhospital ing stations (23.8/12.8); admissions and AERMOD dispersion model (19.2/16.0)
Study findings OR for same-day ED visits: 1.10 (95% CI 1.00–1.22), and hospital admissions: 1.42 (95% CI 1.10–1.82)
OR change due to 10 μg/m3 increase in Henderson et al, Cohort study; Mean PM10 during days of Respiratory or smoke coverage from total PM10 (TEOM) in respiratory hospital cardiovascular 2011 (30); Residents at the admissions: 1.05 (95% CI 1.00–1.10), and physician visits Southeast corner southeast area of BC forest fires; Comparison cardiovascular admissions: 1.00 (95% CI of two methods: and hospital of BC with a reliable 0.96–1.05) TEOM monitoring admissions 92 days: geocodable residenstations (45.9); July to September tial address in health and CALPUFF dispersion 2003 databases; included model (44.2) newborns (n=281,711; 21.6%
The effects of outdoor air pollution on the respiratory health of Canadian children: A systematic review of epidemiological studies Laura A Rodriguez-Villamizar MD MSc1,2, Adam Magico BSc PhD3, Alvaro Osornio-Vargas MD PhD3, Brian H Rowe MD MSc1,4 LA Rodriguez-Villamizar, A Magico, A Osornio-Vargas, BH Rowe. The effects of outdoor air pollution on the respiratory health of Canadian children: A systematic review of epidemiological studies. Can Respir J 2015;22(5):282-292. Background: Outdoor air pollution is a global problem with serious effects on human health, and children are considered to be highly susceptible to the effects of air pollution. Objective: To conduct a comprehensive and updated systematic review of the literature reporting the effects of outdoor air pollution on the respiratory health of children in Canada. Methods: Searches of four electronic databases between January 2004 and November 2014 were conducted to identify epidemiological studies evaluating the effect of exposure to outdoor air pollutants on respiratory symptoms, lung function measurements and the use of health services due to respiratory conditions in Canadian children. The selection process and quality assessment, using the Newcastle-Ottawa Scale, were conducted independently by two reviewers. Results: Twenty-seven studies that were heterogeneous with regard to study design, population, respiratory outcome and air pollution exposure were identified. Overall, the included studies reported adverse effects of outdoor air pollution at concentrations that were below Canadian and United States standards. Heterogeneous effects of air pollutants were reported according to city, sex, socioeconomic status and seasonality. The present review also describes trends in research related to the effect of air pollution on Canadian children over the past 25 years. Conclusion: The present study reconfirms the adverse effects of outdoor air pollution on the respiratory health of children in Canada. It will help researchers, clinicians and environmental health authorities identify the available evidence of the adverse effect of outdoor air pollution, research gaps and the limitations for further research. Key Words: Air pollution; Asthma; Children; Health effects; Respiratory tract diseases
O
utdoor air pollution is a global problem with serious effects on human health (1). In fact, it has been estimated that in 2011, approximately 80% of the world’s population was exposed to air pollution levels that exceeded WHO guidelines (2,3). Air pollution is a complex mixture of compounds that vary greatly depending on the emission sources. Typically, the so-called criteria air pollutants (CAP, which include particulate matter [PM], ozone [O3], lead [Pb], carbon monoxide [CO], sulphur oxides [SOx] and nitrogen oxides [NOx]), are monitored in surveillance air-quality networks. Interestingly, PM itself represents a complex mixture of particles of various sizes and concentrations of soil, metals, organics, inorganics, elemental carbon, ions and endotoxins, among other contaminants (4). Recently, the PM2.5 (PM size ≤2.5 µm in aerodynamic diameter) has been the focus of most outdoor air pollution and health studies due to its ability to penetrate the lung tissue and induce local and systemic effects (4). Based on findings for lung and bladder cancer, the International Agency for Research on Cancer recently classified outdoor air pollution,
Les effets de la pollution de l’air atmosphérique sur la santé respiratoire des enfants canadiens : une analyse systématique d’études épidémiologiques HISTORIQUE : La pollution de l’air atmosphérique est un problème mondial qui a de graves effets sur la santé humaine. Les enfants sont considérés comme très vulnérables aux effets de ce type de pollution. OBJECTIF : Mener une analyse systématique complète et à jour des publications sur les effets de la pollution de l’air atmosphérique sur la santé respiratoire des enfants du Canada. MÉTHODOLOGIE : Les chercheurs ont effectué des recherches dans quatre bases de données électroniques entre janvier 2004 et novembre 2014 pour évaluer l’effet de l’exposition aux polluants atmosphériques sur les symptômes respiratoires, les mesures de la fonction pulmonaire et l’utilisation des services de santé en raison de maladies respiratoires chez les enfants canadiens. Deux analystes ont procédé à l’analyse indépendante du processus de sélection et de l’évaluation de la qualité, au moyen de l’échelle de Newcastle-Ottawa. RÉSULTATS : Les chercheurs ont colligé 27 études hétérogènes sur le plan de la méthodologie, de la population, des conséquences respiratoires et de l’exposition à la pollution atmosphérique. Dans l’ensemble, les études incluses portaient sur les effets indésirables de la pollution de l’air atmosphérique à des concentrations inférieures aux normes canadiennes et américaines. Les effets hétérogènes des polluants atmosphériques étaient déclarés selon la ville, le sexe, la situation socioéconomique et le caractère saisonnier du problème. La présente analyse décrit également les tendances de la recherche à l’égard de l’effet de la pollution atmosphérique sur les enfants canadiens depuis 25 ans. CONCLUSION : La présente étude confirme de nouveau les effets indésirables de la pollution de l’air atmosphérique sur la santé respiratoire des enfants canadiens. Elle aidera les chercheurs, les cliniciens et les autorités en santé environnementale à repérer les données probantes sur les effets négatifs de la pollution de l’air atmosphérique ainsi que les lacunes et les limites de la recherche, et ce, en prévision de prochaines recherches.
as a whole, as a group 1 carcinogen (5). In addition, well-documented associations exist between outdoor air pollution and other health conditions including asthma, cardiovascular diseases, respiratory infections, adverse birth outcomes and additional cancers, such as leukemia (1,6,7). Children are considered to be highly susceptible to the effects of air pollution due to the immaturity of their immune system, the potential for developmental disruption, greater amount of time spent outdoors and, therefore, higher exposure levels, and a relatively high volume of air exchange relative to body mass (8,9). In fact, outdoor air pollution consistently shows an adverse effect on childhood respiratory health, especially on asthma outcomes, with a total estimated health care cost (among 34 countries, including Canada) of approximately US$1.7 trillion in 2010 (10,11). Asthma is one of the top 10 causes of years lost due to disability in male children worldwide (12). The effects of outdoor air pollution on asthma and other respiratory conditions have been the subject of study involving many adult and children populations in Canada and
1School
of Public Health, University of Alberta, Edmonton, Alberta; 2Department of Public Health, School of Medicine, Universidad Industrial de Santander, Bucaramanga, Colombia; 3Department of Pediatrics; 4Department of Emergency Medicine, University of Alberta, Edmonton, Alberta Correspondence: Dr Laura A Rodriguez-Villamizar, Department of Emergency Medicine, University of Alberta, 7.40 University Terrace, 8440-112 Street Northwest, Edmonton, Alberta T6G 2T4. Telephone 780-492-5489, fax 780-407-3982, e-mail [email protected] 282
©2015 Pulsus Group Inc. All rights reserved
Can Respir J Vol 22 No 5 September/October 2015
Air pollution and children’s respiratory health
elsewhere. Air pollution levels in Canada are relatively low and most Canadian cities experience extreme low temperatures. Thus, Canadian studies offer a unique opportunity to examine the effects of more moderate doses of air pollution compared with those experienced in many other nations (13). In addition, Canada boasts one of the highest percentage of foreign-born citizens (14), being a society of mixed languages, cultures and genetic diversity. Recent findings suggest that the influence of genetic diversity on the population’s susceptibility to air pollution is an important factor that should be considered in this field (15). In 2007, a systematic review of air pollution and children’s health in Canada analyzed the results of epidemiological studies published between January 1989 and December 2004 (16). From 11 studies over a 15-year period, the review identified associations between respiratory health effects and at least some CAP measurements. These associations were, however, often weaker than those reported in studies conducted in other countries. This was believed to be due to the lower levels of air pollution in Canada, the lower number of hours spent outdoors during the colder Canadian winters, as well as reduced levels of outdoor air pollution infiltrating into homes, which could act to reduce personal exposure to outdoor air pollution. The objective of the present study was to conduct a comprehensive systematic review of the literature reporting the effects of outdoor air pollution on the respiratory health of children in Canada. We focused on the literature published during the past 10 years to update the previous review, identify new findings on types of associations between air pollutants and childhood respiratory health, and evaluate differences in those associations across Canadian cities.
METHODS
An a priori systematic literature review protocol was developed. The research question addressed in the present review was: what is the effect of outdoor air pollution exposure on respiratory conditions in Canadian children? Respiratory conditions included respiratory symptoms, lung function measurements and the use of health services due to respiratory disease. Search strategy To increase sensitivity, the search strategy used in the previous review (16) was modified. Specifically, four electronic bibliographic databases (MEDLINE, CINAHL, Scopus and CAB abstracts) were searched (Appendix 1). In general, databases were searched with a combination of terms and derived key words including variation to the following basic terms: “air pollution”, “outdoor air pollution”, “asthma”, “respiration disorders”, “respiratory health”, “respiratory symptoms”, “child”, “adolesc”, “youth” and “Canada”. In the MEDLINE search, the names of 16 specific Canadian cities were included to increase search sensitivity. The search strategy was not restricted by language or publication type. A Google Scholar web search was conducted and references of relevant studies were scanned and selected as a complementary search strategy. Study selection and data extraction The criteria for selecting studies included: any observational analytic design; publication date between January 1, 2004 and November 30, 2014; population included and reported data for children up to 18 years of age residing in Canada; exposure(s) included any nonbiological outdoor air pollutant whether measured directly or inferred (ie, by proximity to roadways), with special interest in the CAP (CO, NO2, SO2, O3, and PM10 and PM2.5); and outcomes included health services use (HSU), lung function measurement or self-reported respiratory symptoms. Studies that included a subset or cohort of Canadian children in which the data for the Canadians were not presented separately were excluded. Two reviewers (LR-V and AM) independently screened the identified articles’ titles and abstracts to select the articles for full review, and reviewed citations that were found to be potentially relevant for inclusion. A third reviewer (AO-V) resolved disagreement. Articles selected for full review were screened in a second round to confirm that the inclusion criteria were met. Agreement was measured using kappa (κ) statistics. Data extraction was performed by two reviewers (LR-V and AM) and summarized in standardized tables.
Can Respir J Vol 22 No 5 September/October 2015
Figure 1) PRISMA flow diagram for selection of studies Quality assessment Study quality was assessed using the Newcastle-Ottawa Scale (NOS), which uses an eight-item rating system to evaluate the method of selection of participants, the exposure/outcome assessment, and comparability among study groups (17). Comparability was evaluated by controlling for potential confounders in terms of study design and the type of health effects under evaluation. The Cochrane NonRandomized Studies Methods Working Group recommends the use of the NOS, although the study of its psychometric properties remains in progress (18). The NOS quality scores range from 0 to 9 (0 to 4 = poor quality; 5 to 7 = moderate quality; 8 to 9 = high quality). The NOS has specific formats for cohort and case-control studies only. The cohort study form was used to evaluate noncohort longitudinal studies and the case control form to evaluate case-crossover and cross-sectional studies. Two reviewers (LR-V and AM) independently performed the quality assessment of the included studies and disagreements were discussed and resolved by consensus. Data analysis Descriptive results of the included studies are provided. While quantitative analyses using pooled measures and random effect models were planned, they could not be conducted due to heterogeneity among study populations (children’s age), outcomes and study designs. Kappa statistics and 95% CIs were generated using Stata version 11.1 (StataCorp, USA).
RESULTS
Search results The present review follows the PRISMA recommendations (19). As indicated in Figure 1, the systematic search identified 162 studies. After removing duplicates, initial screening with inclusion/exclusion criteria and full-text review, 27 studies were included. Studies were excluded for a variety of reasons, primarily because they did not report results on Canadian children. Reviewer agreement was substantial for identifying potentially relevant studies (disagreement 22%; κ=0.73 [95% CI 0.70 to 0.75]) and excellent for identifying included/excluded studies in full-text review (κ=0.91 [95% CI 0.78 to 1.00]). Study characteristics The 27 studies that met the selection criteria varied in design, study location, number and type of air pollutants considered, age of children population and respiratory outcome. Tables 1 and 2 summarize the main characteristics and results of the individual studies grouped according to respiratory outcome examined (20-46). Fifteen of the 27 studies included data from Ontario (20,21,24,26,27,29,31,32,35-39,42,44), five used British Columbia (BC) data (22,23,30,34,46), four used Quebec data (28,33,40,41),
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Table 1 Characteristics and results of included studies with health services use outcomes Reference; study location; and study period Lin et al, 2004 (34); Vancouver area; 1987–1998
Study design; study population and size
Pollutants (mean or median levels*) and methods assessing exposure
Respiratory outcome
Hospitalizations Time series study; Mean CO (960), SO2 (4.77), NO2 (18.65), O3 for asthma hospitalizations of (28.02), PM10 (NS), PM2.5 6–12 year olds; from (NS) from 1995-1998; BC Linked Health from monitoring Dataset (n=3822) stations
Adjustment for confounding factors
Study findings
Sex, temperature, RR of asthma hospitalizations in low SES relative humidity, group associated with: NO2 (male, 1-day lag): 1.16 (95% CI 1.06–1.28), NO2 (male 4-day lag): SES, day of the 1.18 (95% CI 1.03–1.34), SO2 (female 4-day week lag): 1.17 (95% CI 1–1.37), and SO2 (female 6-day lag): 1.19 (95% CI 1–1.42)
Yang et al, Case-crossover, Mean CO (700), O3 (14.3), Hospitalizations OR of respiratory hospitalizations associated NO2 (16.8), SO2 (3.5), for respiratory 2004 (46); with 3-day lag mean and max PM10-2.5: case-control and disease (includ- 1.22 (95% CI 1.02–1.48) and 1.14 (95% CI Greater Vancouver; time-series analyses; PM10 (13.3) and PM2.5 (7.7); from local 0.99–1.32), respectively; time-series analysis ing asthma) 1995–1999 first hospital admisgave weaker associations sions of 0–3 year olds, monitors excluding birth-related admissions (n=1610)
Sex, SES, day of the week, season, study year, season and influenza hospitalizations
Sex, temperature, pollutant interactions and seasonality
Lin et al, 2005 (35); Toronto; 1998–2001
Case-crossover design; Mean PM10 (20.41), PM2.5 Hospitalization (9.59), for respiratory hospitalizations of PM10-2.5 (10.86), infections 0–14 year olds CO (1160), SO2 (4.73), (n=6782) NO2 (24.54), O3 (38.06); from monitoring stations
Luginaah et al, 2005 (37); Windsor; 1995–2000
Time series and casecrossover design; hospitalizations 0–14 year olds (n=1602)
Hospitalizations Mean NO2 (38.9), SO2 (27.5), CO (1300), for respiratory PM10 (50.6), TRS (8), and disease coefficient of haze (0.5); from monitoring stations
Time Series RR: NO2: female 2-day lag: 1.19 Temperature, sex, (95% CI 1.002–1.411); SO2: female Current-Day: humidity, baromet1.11 (95% CI 1.011–1.221); CO: female 2-day lag: ric pressure, 1.07 (95% CI 1.001–1.139); Cross-over design seasonality OR: CO: female current day, 2-day lag and 3-day lag: 1.15 (95% CI 1.006–1.307), 1.19 (95% CI 1.020–1.379) and 1.22 (95% CI 1.022–1.459)
Dales et al, 2006 (25); 11 of the largest Canadian cities; 1986–2000
Time series study; hospitalizations of 0–27 day olds (n=8586)
Hospitalizations Mean NO2 (21.8), SO2 (4.3), CO (1.0), O3 for respiratory (17.0), and PM10 (NS); disease from monitoring stations (population weighted average)
Long-term temporal The percentage of variation for IQR increase trends, day of for all gasses combined was 9.61% (95% CI 4.52–14.7); individually: O3: 2.67 (95% CI 0.98– week effects, 4.39); NO2 2.48 (95% CI 1.18–3.8); SO2: 1.41 weather (95% CI 0.35–2.47); CO: 1.3 (95% CI 0.13–2.49) variables, other gases and PM10
Villeneuve et al, 2007 (45); Edmonton; 1992–2002
Case-crossover design Summer/winter ED visits for (time stratified); ED median PM10 (22.0/19.0), asthma PM2.5 (7.0/7.3), CO visits of 2–14 year (600/900), SO2 (2.0/3.0), olds (n=20,392) NO2 (17.5/28.5), O3 (38.0/24.3); from monitoring stations
Temperature, Positive association were observed in warm relative humidity, season and higher in 2–4 years: OR 5-day season, average: NO2 1.50 (95% CI 1.31–1.71), CO 1.48 (95% CI 1.27–1.72), PM2.5: 1.16 (95% aeroallergens, and CI 1.04–1.28) and PM10: 1.16 (95% CI 1.05– ED visits for 1.28); For 5–14 years: OR 5-day average: NO2: influenza 1.13 (95% CI 1.02–1.24), O3: 1.14 (95% CI 1.05–1.24), PM2.5: 1.10 (95% CI 1.02–1.17), PM10: 1.14 (95% CI 1.06–1.22); many of the 1- and 3-day lags were also significant during the warm season for various pollutants
Szyszkowicz et al, 2008 (43); Edmonton; 1992–2002
ED visits for Longitudinal study; Mean/median CO asthma 0–10 years ED visits (700/600), NO2 (21.9/19.7), SO2 (2.6/2.2), (n=18,891) O3 (18.6/17.8), PM10 (22.6/19.4), PM2.5 (8.5/6.2); from monitoring stations
Sex, temperature, Many positive associations were observed in relative humidity, the warm season; the higher percentage increase for each pollutant was: CO (2-day lag) day of the week male: 17.7% (95% CI 10.2–25.6), NO2 (2-day lag) male: 19.2% (95% CI 11.4–27.6), O3 (same day) female: 17.8% (95% CI 7.1–29.5), PM10 (2-day lag) male: 7.4% (95% CI 3.1–11.9), PM2.5 (same-day) female: 7.7% (95% CI 5.2– 10.3), O3 (1-day lag), PM10 (same-day), and PM2.5 (2-day lag) showed positive variations for some age/sex/season combinations
Burra et al, 2009 (20); Toronto; 1992–2001
Longitudinal study; family physician and specialists service claim records for 1–17 year olds (n=1,146,215)
Mean SO2 (9.7), NO2 (39.2), O3 (33.3) and PM2.5 (17.9); from monitoring stations
OR of hospitalizations for 6-day average exposure to: PM10-2.5: boys 1.15 (95% CI 1.02–1.3), girls 1.18 (95% CI 1.01–1.36); PM10: boys 1.25 (95% CI 1.01–1.54); NO2: girls 1.31 (95% CI 1.05–1.63); PM2.5, O3 and SO2 showed no associations
SES, temperature, Asthma RR for pollutants by SES quintiles (Q1/Q5) physician visits were: SO2: 1.005 (95% CI 1.000–1.010), NO2: barometric pres1.002 (95% CI 0.995–1.008), and PM2.5: sure, 24 h mean 1.006 (95% CI 0.997–1.015); low SES groups relative humidity, had higher RR in SO2 and PM2.5 models day of the week
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Air pollution and children’s respiratory health
Table 1 – CONTINUED Characteristics and results of included studies with health services use outcomes Reference; study location; and study period
Study design; study population and size
Smargiassi et al, Case-crossover 2009 (41); design (time Montreal (Quebec); stratified); 2–4 year 1996-2004 olds living near a refinery (n=1579)
Pollutants (mean or median levels*) and methods assessing exposure
Respiratory outcome
Asthma ED Daily peak mean SO2 (east/southwest of visits or refineries) using monitorhospital ing stations (23.8/12.8); admissions and AERMOD dispersion model (19.2/16.0)
Study findings OR for same-day ED visits: 1.10 (95% CI 1.00–1.22), and hospital admissions: 1.42 (95% CI 1.10–1.82)
OR change due to 10 μg/m3 increase in Henderson et al, Cohort study; Mean PM10 during days of Respiratory or smoke coverage from total PM10 (TEOM) in respiratory hospital cardiovascular 2011 (30); Residents at the admissions: 1.05 (95% CI 1.00–1.10), and physician visits Southeast corner southeast area of BC forest fires; Comparison cardiovascular admissions: 1.00 (95% CI of two methods: and hospital of BC with a reliable 0.96–1.05) TEOM monitoring admissions 92 days: geocodable residenstations (45.9); July to September tial address in health and CALPUFF dispersion 2003 databases; included model (44.2) newborns (n=281,711; 21.6%
